motion pictures

...film. The first is to convert the negative silver image that is obtained from a normally exposed film into a positive dye image. The clue to how this can be done came from experience with a developer known as pyro (pyrogallol), once very popular with still photographers. A negative developed with pyro developer has not only a silver image but also a brown stain. Study of the process...

negative and positive film

During development (in a darkroom) the silver salt crystals that have been struck by the light are converted into metallic silver, forming a visible deposit or density. The more light that reaches a given area of the film, the more silver salt is rendered developable and the denser the silver deposit that is formed there. An image of various brightness levels thus yields a picture in which...

Photofinishing laboratories use machines that carry the films in spliced-together lengths or on racks through successive tanks of the processing solutions. Prints are usually made to standard formats on automatic enlargers, taking both the negatives and the paper in continuous rolls. The paper rolls of 250 or 500 feet are processed in continuous-strip processors, which deliver prints dry and...

photoengraving

In the early days of photoengraving, with wet-plate images on a glass support, it was impossible to process photographic images by any means other than immersion in solutions contained in a shallow pan or tray or by dipping into a tank of solution. Such tank and tray processing remains important but is now being supplanted by the use of automatic film-processing machines. Derived from equipment...